Re: [PATCH v5 09/13] LoongArch: Linux ABI

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 07/06/2022 06:32, caiyinyu wrote:
> +static inline ElfW (Addr) __attribute ((always_inline))
> +elf_ifunc_invoke (ElfW (Addr) addr)
> +{
> +  return ((ElfW (Addr) (*) (void)) (addr)) ();
> 
> At least for RISCV, sparc, aarch64, powerpc, arm; the ifunc resolver expects
> a unsigned long int begin the hardware capability from kernelk (AT_HWCAP).
> 
> AArch64 also extends it by passing both uint64_t and a struct with both
> AT_HWCAP and AT_HWCAP2.  I am not sure if loongarch will ever use more
> than the AT_HWCAP.
> *Currently ifuncs (like __memchr_ifunc, __memcpy_ifunc ...) are not used in loongarch, and we will add these in future.*
> *or we can add the following patch (now **AT_HWCAP only) though not woking: ****>>>>>>>>>>>*
> 
> diff --git a/sysdeps/loongarch/dl-irel.h b/sysdeps/loongarch/dl-irel.h
> index 0dfe78c217..ef248095b9 100644
> --- a/sysdeps/loongarch/dl-irel.h
> +++ b/sysdeps/loongarch/dl-irel.h
> @@ -21,13 +21,18 @@
>  
>  #include <stdio.h>
>  #include <unistd.h>
> +#include <ldsodefs.h>
> +#include <sysdep.h>
>  
>  #define ELF_MACHINE_IRELA 1
>  
>  static inline ElfW (Addr) __attribute ((always_inline))
>  elf_ifunc_invoke (ElfW (Addr) addr)
>  {
> -  return ((ElfW (Addr) (*) (void)) (addr)) ();
> +  /* The second argument is a void pointer to preserve the extension
> +     fexibility.  */
> +  return ((ElfW(Addr) (*) (uint64_t, void *)) (addr))
> +        (GLRO(dl_hwcap), NULL);
>  }
>  
>  static inline void __attribute ((always_inline))
> 
> *<<<<<<<<<<<<<<<<<<*

AArch64 added the extra argument to preserve backwards compatibility, which
is not the case here.  Since ifunc is also used outside glibc, maybe it would
be better to  use the extendable struct as default:


 struct __ifunc_arg_t
 {
   unsigned long int _size; /* Size of the struct, so it can grow.  */
   unsigned long int _hwcap;
 };

 static inline ElfW (Addr) __attribute ((always_inline))
 elf_ifunc_invoke (ElfW (Addr) addr)
 {
   __ifunc_arg_t arg = 
   {
     ._size = sizeof (__ifunc_arg_t),
     ._hwcap = GLRO(dl_hwcap),
   }
   return ((ElfW(Addr) (*) (uint64_t, void *)) (addr)) (&arg);
 }

And then export __ifunc_arg_t on the sys/ifunc.h header like aarch64.